Climate activist Greta Thunberg has tweeted a photo of herself sitting on the floor of a German train surrounded by lots of bags.

She posted the tweet late Saturday with the comment: “Traveling on overcrowded trains through Germany. And I’m finally on my way home!”

Some Twitter users pitied the 16-year-old Swedish activist for not being able to get a proper seat on the train for the long ride home from Madrid, where she was attending the UN climate change conference.

They wished her a safe trip home after months of travelling by trains and boats to different climate events in Europe and the US.

The activist does not fly on planes because it is considered harmful to the climate.

She was recently named Time magazine’s Person of the Year for her efforts to prod government and others to take faster actions in fighting climate change.

German railway operator Deutsche Bahn has come under fire in recent years for delays, last-minute train cancellations and expensive ticket fares.

Deutsche Bahn replied to the teenager’s tweet, wishing her a good trip back home, adding “we continue working hard on getting more trains, connections and seats.”

In the picture on Twitter, Greta is sitting on the floor at the end of a rail car with her back leaning against a suitcase, staring out of a window.

There’s an empty food box next to her and more suitcases and backpacks piled up by her side.

Later on Sunday, Deutsche Bahn tweeted twice more in regard to Greta’s train travels through Germany.

In the first tweet, the company thanked the teenager for supporting Deutsche Bahn’s battle against climate change and pointed out the train she used had been running 100% on eco-friendly electricity.

In the second tweet, Deutsche Bahn seemed to suggest Greta had not spent the entire train ride sitting on the floor.

The company pointed out to the teenager that “it would have been even nicer if you had also reported how friendly and competently our team served you at your seat in first class”.

Greta later tweeted the fact she did not first sit in a seat was not meant as a knock against Deutsche Bahn.

She wrote: “This is no problem of course and I never said it was. Overcrowded trains is a great sign because it means the demand for train travel is high!”